docs: def standardized_compound(self):
          """Return the :class:`~pubchempy.Compound` that was produced when this Substance was standardized.
  
          Requires an extra request. Result is cached.
          """
          for c in self.record['compound']:
              if c['id']['type'] == CompoundIdType.STANDARDIZED:
                  return Compound.from_cid(c['id']['id']['cid'])